Electronic systems, such as multicard computer structures, individually or in other structures such as communications systems, usually consist of a set of cards sharing a common bus structure, often referred to as a "backplane". Depending upon the nature of the system, various types of reset structures are employed. The basic form provides one or more cards with circuitry which can generate a reset signal that will cause all cards on the backplane to enter a reset state. This type of reset is undesireable because all processes must stop, and begin again at the reset point. A great amount of time and information can be lost.
More sophisticated systems allow the selective resetting of individual cards. This allows a card which is not operating properly to be retrieved from some undesireable state that does not respond to normal communication attempts to restore its operation. All other cards should continue to operate without being effected. Selective resetting in the prior art requires each card to be assigned a unique address. A card is then reset by generating the assigned address on the backplane bus, along with a reset signal of some type. This type of selective reset is undesireable in a number of respects:
1. It requires a portion of the address space to be allocated for the reset purpose.
2. It assumes that the backplane is available for the reset operation.
3. It requires circuitry on each card to decode this unique address and may, in some circumstances, add drive requirements to the bus masters for circuitry which has no other benefit.